"Beer apples"

Does anyone know what "beer apples" are properly called?
They're not quite a normal flowering crab. The fruit is about 1.5" by 1" (or a little larger), oblong rather than round, a distinctive odd shade of red skin, tends to be reddish inside, has a delightful strong tart flavour, and will make you sick if you eat too many of them raw :) but makes the world's most wonderful jelly, and they have a long and productive bearing season.
The trees are seen occasionally in Montana, but they are rare; have not seen them elsewhere (I'm now in Calif.) They're big vigorous hardy trees with heavier branches than most apple trees; I strongly suspect all the ones I've seen are own-root.
I'd settle for getting some seeds that might be "close enough" to type, if I can't find the real thing.
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